On a basic level, Scout represents Harper Lee, and Lee even admits to writing To Kill a Mockingbird as a semi-autobiographical novel. From a young age, Harper Lee went by her middle and last name, choosing not to be called by her first name, Nelle. (She was named after her grandmother, Ellen -- "Nelle" spelled it backwards, of course.) In addition to opting to go by the less feminine name, she also dressed as her character Scout did, in overalls and other "masculine" clothes, described as "a rough 'n tough tomboy" (eNotes).
Also, Lee's childhood friend Truman Capote was her inspiration for the character Dill. In her novel, Lee created a smaller-than-average young boy (Capote was also known for being diminutive) who lived next door during the summers (Capote's family almost always sent him to live with his cousins in the summer, which happened to be right next door to Lee's house).
Also, as critic Rebecca Best claims,
[...] Scout realizes that the option of changing one's status in society [...] is not available to poor whites like Mayella Ewell and blacks like Robinson (550).
Harper Lee also realized, very early in her life, that certain people were not afforded the same status as others. She was a child during the famous Scottsboro Trials, during which nine young African-American men went through a series of arduous trials concerning the rape of a white woman -- a rape none of them committed. She also lived in a community much like the fictitious town of Maycomb, surrounded by those of varying social classes who had to struggle to climb the social ladder.
Beyond these parallels, most other similarities between Scout Finch and Harper Lee are purely speculative.
Additionally, Harper Lee's father, Amasa Coleman Lee, was the inspiration for Atticus Finch. Both an attorney and Alabama state legislator (1927-1939), Lee served his local constituents during the same approximate time as Atticus. Frances, Harper Lee's mother, was the inspiration for two families in the novel: Her maiden name was Finch, and her middle name was Cunningham. Her name may also have been the basis for Scout's cousin Francis. Like Atticus, Harper Lee attended school in Montgomery (at Huntingdon College) and, later, the University of Alabama, where other members of the Finch family went to school. And, according to Truman Capote (the inspiration for Dill), there was a real life character in Monroeville who left the children gifts in trees, just like Boo Radley.
"In my original version of Other Voices, Other Rooms I had that same man living in the house that used to leave things in the trees, and then I took that out. He was a real man, and he lived just down the road from us. We used to go and get those things out of the trees. Everything she wrote about it is absolutely true."